The invention relates to a rollover-sensing system, and particularly to a rollover-sensing system that senses trip rollover events, and activates at least one safety device in response to sensing the trip rollover event.
Vehicle rollover events are situations where vehicle occupants are at risk of serious injury. To reduce the risk of injury, a vehicle may include a rollover sensing system that senses when a vehicle rollover event occurs, or more precisely, senses the occurrence of conditions that are indicative of a rollover event occurring. A rollover event occurs very quickly and in order to activate safety devices in time to protect vehicle occupants, a rollover sensing system must act at the beginning of the event. In use, most systems make decisions based on data that indicates that the vehicle will or is likely to rollover. Nevertheless, such systems are often explained in terms of detecting the occurrence of a rollover event even though the systems act before the vehicle has fully rolled over. This convention is followed in the discussion below.
Rollover events can be categorized in three groups. An upward rollover event occurs when the vehicle is traveling in a forward direction, and then travels across an object or an inclined surface resulting in an upward roll. A downward rollover event occurs when the vehicle is traveling in a forward direction, and then travels across an object or a declinated surface resulting in a downward roll. A third type of rollover event is a xe2x80x9ctripxe2x80x9d rollover event. The trip rollover event occurs when the vehicle is initially traveling in a forward direction, rotates about the z-axis of the vehicle such that the vehicle is xe2x80x9cslidingxe2x80x9d sideways, and travels or xe2x80x9ctripsxe2x80x9d across an xe2x80x9cobjectxe2x80x9d resulting in a vehicle roll. The object may be a curb, a depression, a location where there is a change in the coefficient of friction of the surface upon which the vehicle is travelling, or a similar item.
Some prior rollover-sensing systems sense upward or downward rollover events. Most vehicle manufacturers typically require that one or more safety devices be activated approximately 700 ms after the upward or downward rollover event begins. However, for trip rollover events, vehicle manufacturers requires that safety devices be activated within approximately 200 ms. One reason for the shorter activation time in trip rollover events is that such rollovers cause the occupants to continue moving sideways at great velocities. Unless the occupants"" speed is reduced, they may collide into a side window or eject from the vehicle. In order for the system to deploy a safety device quickly, the trip rollover event requires faster fire or activation times. Prior rollover-sensing systems are unable to consistently predict likely trip rollover events such that the system activates safety devices within the required activation time.
Accordingly, in one embodiment, the invention provides a rollover sensing system designed for use with an overland vehicle with x, y and z-axes and a frame. The system includes an accelerometer connected to, or mounted on or in the frame. The accelerometer is operable to generate a y-acceleration signal representative of the acceleration of the vehicle in the direction of the y-axis. The system also includes an angular-rate sensor connected to, or mounted on or in the frame. The angular-rate sensor is operable to generate an angular rate signal representation of the angular velocity of the vehicle about the x-axis. The system also includes a processor such as a microcontroller and coupled to the accelerometer and the angular-rate sensor. The microcontroller is operable to receive the y-acceleration signal and the angular-rate signal and calculate a vehicle angle having a relationship to the angular-rate signal. The calculated vehicle angle is representative of the angle of the vehicle about the x-axis. The microcontroller also determines an angular-rate threshold having a relationship to the vehicle angle and the y-acceleration signal, compares the angular-rate signal to the angular-rate threshold, and generates an output signal when a magnitude of the angular-rate signal is greater than the angular-rate threshold. The output signal is preferably transmitted or sent to a safety device of the vehicle. The safety device is activatable in response to receiving the output signal.
The invention also provides a method of activating a safety device of a vehicle having x, y and z-axes. The method includes generating a y-acceleration signal representative of the acceleration of the vehicle in the y-axis, generating an angular-rate signal representative of the angular velocity of the vehicle with respect to the x-axis, and calculating a vehicle angle having a relationship to the angular-rate signal and being representative of the angle of the vehicle about the x-axis. The method also includes determining an angular-rate threshold having a relationship to the vehicle angle and the y-acceleration signal, comparing the angular-rate signal to the angular-rate threshold, and activating a safety device when a magnitude of the angular-rate signal is greater than the angular-rate threshold.
The microcontroller determines an angular-rate threshold having a relationship to the y-acceleration of the vehicle in the direction of the y-axis, and the angle of the vehicle about the x-axis. Using both the y-acceleration and the angle for calculating the angular-rate threshold reduces the firing times for activating safety devices. For example, if the y-acceleration is high, which signifies a trip rollover event, then the rollover-sensing system of the invention reduces the angular-rate threshold, allowing the safety device to activate earlier than if the y-acceleration is low. This results in the system being more responsive to a trip rollover event.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.